1. Field of the Invention
The invention is directed to a device for radiographically testing the weld of elongate, welded hollow bodies of metal, in particular steel pipes, without the use of film.
1. Discussion of Prior Art
In X-ray testing of the weld of elongate, welded hollow bodies of metal, aside from the classic method using film, there is also a growing interest in non-film methods which make use of image converters. In this method, the X-rays penetrating the seam of the hollow body in the direction of thickness impinge on a radiation-sensitive sensor which converts the occurring radiation energy into electric signals which are then processed in a computer. In so doing, it is unimportant from the point of view of the actual measurement process whether the liquid-cooled X-ray tube is arranged inside or outside the hollow body. In hollow bodies of smaller dimensions, i.e. less than approximately 600 mm clear width, this freedom of choice no longer exists, since an image converter having a cross section of substantially greater dimensions than the X-ray tube could no longer be accommodated inside the hollow body. Moreover, because of the curvature of the pipe wall in the case of a pipe, there is always a minimum distance between the input screen of the image converter and the weld to be tested which is determined by the pipe radius and the geometry of the X-ray image converter. A geometrical blurring which impairs the quality of the image can result due to the finite magnitude of the focal spot of the X-ray tube.
The fundamental standards for acceptance tests of welded steel piping, particularly large pipes, dictate that both end regions of the pipe be tested in a length of at least 200 mm. Moreover, all weld seams for which readings were obtained in prior ultrasonic testing must be checked by means of X-ray. This means that every portion of the entire weld length must be capable of testing, which necessitates a corresponding displacement of the X-ray tube relative to the hollow body.
In stationary X-ray tubes the hollow body must be moved axially. This is a disadvantage as the concrete shielding must then have a length at least twice that of the longest hollow body to be tested. This is also the case when the X-ray tube is moved, since the high-voltage generator having large cross-sectional dimensions cannot be inserted into the pipe along with the X-ray tube and the high-voltage cable or, in the case of a two-pole X-ray tube, the high-voltage cables and the other supply lines between the high-voltage generator and X-ray tube must be at least twice as long as the longest hollow body to be tested. When the hollow body has a length of more than 12 m, such an arrangement cannot be used regardless of the cost of a longer concrete shielding, since the length of the high-voltage cable is limited to approximately 25 mm for reasons pertaining to load. A possible solution with respect to a short length of the concrete shield would be to wind the high-voltage cable and other supply lines on to a large drum, wherein the high-voltage generator would also have to be rotated. Such winding would mean a high mechanical loading of the thick and inflexible high-voltage cable. Moreover, the rotation of the generator would cause problems with the connections of the control lines and supply lines. Difficulties would also arise with regard to the coolant supply and the system would be highly prone to disturbance.
It is therefore an object of the present invention to provide a device for radiographically testing, without film, the weld of elongate, welded hollow bodies such as steel pipes which is not susceptible to disturbances.
It is a further object of the present invention to provide a testing device suitable for use with hollow bodies having a small clear width and lengths of more than 12 m.
It is yet another object of the present invention to provide a testing device for which a concrete shield only slightly longer than the longest hollow body to be tested is adequate.